Containerized frozen whipped toppings are commonly made today by a process that includes the following sequential steps:
(a) forming a mixture comprising water, water-soluble carbohydrate, fat, protein, emulsifying agent, and thickener;
(b) pasteurizing the mixture;
(c) homogenizing the mixture to form an oil-in-water emulsion;
(d) cooling the emulsion at a temperature in the range of about 27 to 45xc2x0 F.;
(e) holding the emulsion at a temperature in the range of about 27 to 45xc2x0 F. for a long enough time to allow at least some of the fat to crystallize;
(f) aerating and whipping the emulsion, under superatmospheric pressure, into a topping;
(g) dispensing the topping into containers; and
(h) freezing the topping while in the containers.
Steps (f) and (g) typically are performed in a continuous manner, with an unbroken flow path from the aeration of the liquid emulsion to the dispensing of the finished whipped topping.
In the early days of making frozen whipped toppings by such a process, both the aerating and the whipping was done in one intermeshing pin mixer with internal recirculation, e.g., a Votator continuous recirculating mixer. (See, e.g., the process described in U.S. Pat. No. 4,451,492.) The construction and operation of such mixers are described, for example, in U.S. Pat. No. 3,251,577, which is hereby incorporated by reference. The single-step aeration/whipping operation had a drawback, however, in that it was difficult to achieve consistent results, which is important for consumer satisfaction. For example, it is usually desired to achieve about the same level of overrun (say, for example, an overrun of about 275 percent) from one hour to the next and from one day to the next. Overrun is the amount by which the volume of the emulsion is increased, due to the aerating and whipping. The greater the overrun, the lighter is the topping. Such consistency proved difficult to achieve with the single-step aeration/whipping operation. As a result, the weight of the contents of a standard size container could vary significantly, even though they were produced only minutes apart.
In answer to that problem, the process was modified by performing the aerating/whipping operation in two steps, under substantially different pressures. First the emulsion was aerated in an intermeshing pin recirculating mixer under a back pressure of at least 40 psig. Then the pressure was gradually reduced by about 10 to 50 psig, following which the emulsion was whipped in a scraped-surface heat exchanger under a back pressure of about 20 to 70 psig. (See, for example, the processes described in U.S. Pat. Nos. 4,478,867 and 5,077,076.) A scraped-surface heat exchanger is a device with a chamber through which product is pumped, using a rotor with radial arms ending in devices that scrape the inner wall of the chamber, as the rotor turns. Exterior to the chamber is a cooling jacket, which, when activated, can so chill the contents of the chamber that, when an aqueous liquid is being pumped through the chamber, ice crystals will form on the inner chamber wall. The scraping action and turbulence in the chamber distributes those crystals throughout the product.
While good overrun consistency can be achieved by the two-step aeration/whipping procedure just described, it would be desirable if there were an alternative that did not employ such high pressures. The greater the pressure used, the greater the concern for worker safety. Also, higher pressures mean greater wear on operating equipment such as pumps, as well as greater energy consumption.
We have discovered that good overrun consistency can be achieved with a process as described, without having to use back pressures as high as 40 psig or more, if the aerating/whipping operation is performed using two turbulent mixing zones, in which a higher average shear rate is used in the second zone than in the first. Essentially, this new aerating/whipping operation involves the following steps:
(i) adding aeration gas to the cooled emulsion,
(ii) subjecting the gas-containing emulsion to turbulent mixing in a first mixing zone, for a time sufficient to disperse the gas in the emulsion and raise the viscosity of the emulsion, and
(iii) subjecting the resultant emulsion to further turbulent mixing in a second mixing zone, using a higher shear rate than used in the first zone, for a time sufficient to achieve an overrun value of at least about 175 percent.
By performing the aeration/whipping operation in this manner, it is possible, we have found, to achieve good product consistency without having to use back pressures as high as 40 psig at any stage in the process. By the use of such low pressures there is less chance of worker injury in the case of a break in one of the lines that is under pressure. Also, there is less energy consumption, and the rate of wear on certain pieces of the equipment, such as pumps, is reduced.